Escherichia coli (EPEC) is one of the five
virotypes (classes) of
pathogenic E. coli and is known to be
the cause of diarrheal diseases. Nonpathogenic
E. coli is a Gram-negative, rod-shaped
bacterium (appears as red/pink colored rods upon Gram staining),
known for its ability to extensively colonize the
gastrointestinal tract of warm-blooded mammals and serve
the useful task of keeping other bacterial
organisms in check (Figure 1). No E.
coli is capable of sporulating.
Magnified 600X, this fluorescent antibody
stained photomicrograph revealed the presence of
enteropathogenic Escherichia coli
bacteria, which were found in a fecal smear from
an infant with diarrhea. E. coli is a
member of the family of bacterial organisms
within the family Enteribacteriaceae, and
contains the highly pathogenic strain, which has
been given the label O157:H7.
EPEC forms microcolonies on the surface of the
intestinal epithelial cells (Ochoa
2008); individual bacterial cells have the
length of approximately 2 μm and a diameter of
0.5 to 0.7 μm. It is considered to be a
non-invasive pathogen and employs type three
secretion system (T3SS) to deliver its proteins
into the host epithelial cells (Dean & Kenny,
2009) (Figure 2). EPEC is a facultative anaerobe (as all
members of the order Enterobacteriales); in
anaerobic conditions it is capable of obtaining
energy either by means of fermentation or by
anaerobic respiration (with NO3,
and fumarates serving as final electron
acceptors instead of O2).
EPEC, as opposed to many other species of
lack fimbriae. It is known to express type IV
pili, instead, which are associated with the
twitching motility of this pathogenic strain.
Figure 2. Many bacteria use
Type-III secretion systems to inject toxins into
host cells (Pier et al., 2002).
Click to enlarge.
Virulence and Pathogenicity: Key virulence factors of
this pathogen – plasmid encoded protein EPEC
adherence factor (EAF), which allows for
adherence of the bacteria to the intestinal cell
walls. Another adhesion factor that serves as a
virulence factor as well is called intimin (a
non-fimbria adhesion) and is responsible for the
final stages of adherence. EPEC is responsible
for creation of characteristic lesions at the
sites of adhesion to GI tract (Figure 3,
Figure 3. Attaching and effacing lesion showing
effacement of microviili (mv) and pedestal
(star) with adherent EPEC (arrow).
Main mode of pathogenic action is being linked
with EPEC’s interference and disruption of the
normal host signal transduction, but not a
toxin. production (the process of cell adhesion
is also named as a reason for pathogenic effects
of the strain); EPEC when attached to the
intestinal epithelial cells is also capable of
causing inflammation at sites.
The process of cell adherence is very
characteristic and involves very active
recruitment, restructuring and polymerization of
the host cell’s actin at the site of attachment
(pedestal) by the bacterial cell – phenomenon
has been named 'attaching and effacing' (Figure 3,
Adherence patterns of enteropathogenic
E. coli (EPEC) strains. Localized
adherence (LA), diffuse adherence (DA),
aggregative adherence (AA), and localized
(Trabulsi et al., 2002).
Infections and Diagnostics:
EPEC is known to cause
watery and/or bloody diarrhea (dysentery), which is a main
cause of diarrhea in children in developing
countries (mainly under two years of age);
infection usually occurs via consumption of
improperly treated drinking water and sometimes
meat products. Transmission of EPEC has been
also reported by contact with domestic animals.
The most widely
used diagnostic techniques for EPEC include the
use of monoclonal antibodies against Bfp, the
pili expressed by EPEC used by the pathogen for
adhesion purposes). Remarkably, Bfp genes of
EPEC have been shown to be 100% specific to this
pathogen and could not be PCR amplified in any
other known bacterial enteropathogens. More trivial
symptoms of the disease (diarrhea, commonly
lasting for as long as two weeks, often with
blood) can be used to identify the EPEC as a
possible cause of the condition.
Dean, P., & Kenny,
B. (2009). The effector repertoire of
enteropathogenic E.coli: ganging up on the host
cell. Current Opinion in Microbiology,
Barletta, F., Contreras, C., & Mercado, E. (2008).
New insights into the epidemiology of
enteropathogenic Escherichia coli infection.
Transactions of the Royal Society of Tropical
Medicine and Hygiene, 102(9): 852-856.
Keller, R., & Gomes, T.A.T (2002). Typical and
atypical enteropathogenic Escherichia coli.
Emerging Infectious Diseases, 8(5).